This is our revised application in response to Program Announcement PA-06-538 that specifically aims to stimulate research on host response to microbial biofilms leading to improved strategies for diagnosing, preventing, and treating biofilm-associated infectious diseases. We propose to investigate the effects of key molecules used by microbes to coordinate biofilm formation, namely bacterial quorum sensing (QS) factors, on cells of the host innate immune system. Biofilms are clinically important, accounting for over 80 percent of microbial infections in the body. The importance of bacterial QS factors in biofilm formation is supported by a large body of in vitro and in vivo data resulting from genetic, biochemical and biological studies with Gram-negative and Gram-positive organisms. QS factors are small, diffusible molecules of different chemical classes that include the AHL series, oligopeptides, and the ribose-derived DPD/AI-2 molecule. The presence of QS factors in biofilms is well documented. In addition, biofilms release a multiplicity of other biologically active, bacterially-derived molecules, such as bacterial lipopolysaccharides (LPS), peptidoglycan fragments, and bacterial DNA, into the local environment. These bacterial products stimulate the host innate immune response via receptors that include those of the Toll-like receptor (TLR) and the Nod-like receptor (NLR) families. Yet despite the presence of normal systemic immune function, biofilms still form. This paradox may be due to bacterial factors that lead to a local suppression of normal innate immune mechanisms. Thus, we hypothesize that in the micro-environment of the oral cavity or in other sites where biofilms form, one or more classes of QS factors may contribute to immune dysfunction through direct or indirect effects on host cells. Based on our recently published data, we postulate that some QS factors are anti-inflammatory in their actions on host cells;however, other QS factors might act in a pro-inflammatory manner. The experiments outlined here will evaluate which members of the QS factor classes have the ability to modulate normal host innate immune responses, to understand the underlying molecular mechanisms of this modulation and will, ultimately, provide information needed to develop new therapeutic strategies. This application brings together two highly regarded research groups located at The Scripps Research Institute - the Ulevitch group with many years of expertise in studies of fundamental mechanisms of innate immunity and the Janda laboratory that is internationally recognized for its work on the chemical synthesis of QS factors. We believe this collaboration will bridge a major gap in our understanding about how processes leading to biofilm formation as well as the biofilm itself influences host immunity. Project Narrative: Biofilm formation in man is present in a majority of disease states where chronic bacterial infection leads to tissue destruction and loss of organ function. This includes diseases as diverse as dental caries and loss of pulmonary function in cystic fibrosis. This proposal is designed to bridge the gap in our knowledge about bacterial-derived biofilms influence the host immune response in the micro-environment where infections occur. The specific focus is on bacterial quorum sensing factors that are essential signals for biofilm formation by the microbe and that we have recently shown have profound effects on host immunity. By further identifying the underlying mechanisms whereby quorum sensing factors may influence host immunity we expect to design new therapeutic approaches to treating chronic infection in man.